I agree that it's better to gain on primal wholefoods. If she gains purely through eating more junk, she'll just go from skinny to skinny fat, which is probably worse. And though she obviously shouldn't eat low carb, it sounds like she needs to eat a lot more healthy fats and protein.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.